In many blinding retinal diseases, the cells that first detect light disappear while much of the neural machinery behind them survives. That preserved circuitry has now been turned into a therapeutic opportunity.
Researchers at the Institute for Bioengineering of Catalonia (IBEC) and a multi-institution consortium have developed photoswitchable small molecule drugs that restored important visual responses in animal models of blindness. The compounds, called prosthe6, are designed to perform part of the job normally handled by photoreceptors — and they work as simple eye drops.
The findings, published in the Journal of the American Chemical Society, show that two compounds in particular — prosthe6-12 and prosthe6-15 — produced especially encouraging results. In blinded zebrafish larvae, the drugs restored saccadic eye movements. In mouse models of age-related macular degeneration and retinitis pigmentosa, the compounds restored an instinctive light avoidance response.
Mice with normal vision naturally favor darkness and avoid brightly illuminated spaces. Blind mice no longer distinguish between the two. After receiving prosthe6, the blind mice again displayed a spontaneous preference for darkness — indicating they could detect light and use that information to guide their movements. No training was required, and the response appeared under ordinary indoor lighting.
The compounds work by targeting a protein called mGlu6 on ON bipolar neurons, retinal cells that normally receive information from photoreceptors. When light reaches the eye, the prosthe6 molecules change shape and trigger activity inside the retina that mimics the signaling normally initiated by photoreceptors. In effect, the drugs function as molecular prostheses, substituting for signals from the missing cells.
Critically, the compounds respond to normal visible or white light. Unlike some optogenetic approaches, they do not require specialized high-intensity light sources. Their small, water-soluble structures allow them to react under daylight or typical indoor lighting conditions.
These molecules do not cure blindness, because they do not address the cause of photoreceptor degeneration, explains Pau Gorostiza, ICREA Research Professor at IBEC and co-leader of the study. But they are remarkably effective at restoring sight, and they do so using a very simple and potentially patient-friendly approach.
The work builds on more than ten years of research and involved scientists from six Spanish research institutions. The technology is patent-protected, and the team is working with Eyelumina, a spin-off company being formed to attract investment for translational research and eventual clinical trials.
Human testing has not begun, and whether the benefits observed in animals will translate to people remains unknown. But if future human studies are successful, this drug-based approach could provide a more accessible and affordable option than current vision restoration technologies — particularly for the estimated 200 million people worldwide affected by conditions involving photoreceptor degeneration.
